Transcript Status Report of the measurement of ´ n) G via

Status Report of the measurement of
GEn via 3He(e,e´ n)
Robert J. Feuerbach
The College of William and Mary
for the E02-013 Collaboration
Elastic EM Form Factors
For an extended spin-1/2 particle, the general vertex term is:
Elastic cross-section:
Or in terms of the
Sachs Form factors:
Dominate at large Q2
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Double Polarization Measurement
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Exclusive QE scattering: 3He(e,e’n)
E02-013 Setup
n
scintillator
~85% polarization
~50%
veto
e
e’
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Running conditions
• 75 msr BB,
~100 msr ND
• Ltotal ~ 5·1036/(cm2 s)
Len ~ 5·1035/(cm2 s)
• BB trigger ~ 2.3 kHz
ND trigger ~ 2.5 MHz
• MWDC ~ 2.6 MHz/uA
20 MHz per plane
E02-013 Status
• Target polarization ~50%
• Beam polarization ~84%
• Electronic LT ~ 82%
• DAQ LT ~ 84%
• Average 4 extra hits per
plane affected tracking
(See Seamus’s talk
Saturday)
January 4, 2006 Hall A
Collaboration Meeting
Assignments
Analyze Q2=1.8 GeV2 dataset
All the students
Calibrate other datasets
ND timing (Jon), BB scint. (Ameya),
Shower/preshower (Sergey),
beam Raster + DC offsets (Brandon)
BB optics (Seamus), Target (Aidan)
Analysis of all datasets: shared
Each student has 1-2 datapoints as primary
responsibility, and one more as a “check”:
each Q2 has 3 students on it.
Veto efficiency ( proton mis-ID)
Jon
ND stability over time
Tim
EPICs and Target conditions database
Brandon
Monte-Carlo for background studies
(pion production, etc.)
Gregg Franklin
Overall Analysis software
Rob
Finite acceptance effects (understood)
Gregg
ND documentation (~ done)
Tim/Albert(geom), Rob(algorithms)
BB geom and algorithms (~ done)
Seamus
Electronics config. doc. (~~ done)
E02-013 Status
Sergey(BB), Alexandre(ND)
January 4, 2006 Hall A
Collaboration Meeting
Electron arm reconstruction
• Preshower/shower
selects electrons well
• Momentum σ ~.9%
@ 1.3 GeV/c on average
• VertexZ σ ~ 4mm
• “super-elastics” due to
imperfect optics
• Scintillator σt ~ 360ps
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Neutron Detector
• Data shown are from an analysis of the 1.8 GeV2 dataset.
• Neutron Detector timing resolution of σ ~ 400ps
• Neutrons/Charged particles differentiated by matching hits in Veto to
clusters in the ND.
• 1/β calculated from time of hit at ND and Rf-corrected time from BB
scintillators.
3He(e,
e’ A) – all charged ND-particle events
protons
Fast pions/muons?
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
QE Event Selection
• Use missing 3-momentum to select QE
events
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
QE Event selection: Protons
Nuclear effects (FSI) can distort the observed asymmetry … Pperp < 150 MeV/c
Momentum distribution
of nucleons in 3He
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
QE Event selection: Neutrons
Neutrons
Accidental
Background
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
QE Event selection: Neutrons
Accidental Background
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Rough Asymmetries @ Q2 = 1.8 GeV2
Integrated Asymmetries (NOT corrected for many several %-size effects) for different
Beam ½-wave plate settings and Target polarization direction changes.
Yet need to account for
distortion of the
asymmetry from
•False asymmetries:
Electronic LT (~.5%)
Tracking eff (~.2%?)
DAQ livetimes(<.1%)
Beam Charge
(<.02%)
•Finite acceptance
•Dilution factors from
N2
proton mis-ID
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Projected Results
Projected error bars assume
results match the
Galster parameterization.
Systematic uncertainties for highest Q2 point still smaller than shown statistical uncertainty.
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
The Future: GEn @ 4.5 GeV2?
• E0=3.7 GeV/c, E’=1.3 GeV/c, θBB=59° to measure GEn/GMn
@ 4.5 GeV2 (limit of CLAS data on GMn).
• Add shielding along beamline for the ND: reduces its rate by
factor of 2.
• Larger cell size to remove halo effects: drop overall rate factor 3.
• Triple Ib to 24uA  Len~1.5 1036 /(s cm2).
• A measurement with the 20% relative statistical uncertainty (vs.
14% at 3.4 GeV2) could be done in 500hrs (25 days).
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Summary
• Electron and neutron detector analysis is well
understood, though still being “tweaked”
• Can identify quasi-elastic proton and neutron events to
extract the asymmetry and GEn.
• Presently analyzing the 1.8 GeV2 dataset to identify
problem areas: so far found electronic deadtime and
tracking eff. (surprises), and proton mis-ID to be
leading corrections.
• Plan to complete 1.8 GeV2 analysis this spring, and
results from all datasets by late 2007/early 2008 (my
estimate).
• Investigating measurement at 4.5 GeV2 ?
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Backup slides
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Proton Asymmetry
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Background Asymmetry
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Data Quality
Beam polarization ~84%
Target polarization ~50% IN BEAM
(Q2~3.5 GeV runs)
• The experiment ran for 3 months in Spring 2006.
• Four datasets (Q2=1.4, 1.8, 2.4, 3.4 GeV2) were taken.
• Commissioned BigBite precision detector package, BigHand, hybrid
cell and advanced optics system for the target.
• Novel holding field magnet and compass to control and understand
field gradients at the target.
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
World data on GEn
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting
Data Analysis
•
•
•
“Results” shown are from an advanced preliminary analysis of the 1.8 GeV2
dataset.
“Neutrons” are ALL clusters in BigHand without matching veto hits (very
loose criteria for now).
Achieved momentum resolution from BB of dp/p~0.8%, BigHand timing
resolution of 400ps (sigma)
3He(e, e’ N)
E02-013 Status
January 4, 2006 Hall A
Collaboration Meeting